Nonwoven fabrics and their manufacture have been the subject of extensive development resulting in a wide variety of materials for numerous applications. For example, nonwovens of light basis weight and open structure are used in personal care items such as disposable diapers as liner fabrics that provide dry skin contact but readily transmit fluids to more absorbent materials which may also be nonwovens of a different composition and/or structure. Nonwovens of heavier weights may be designed with pore structures making them suitable for filtration, absorbent and barrier applications such as wrappers for items to be sterilized, wipers or protective garments for medical, veterinary or industrial uses. Even heavier weight nonwovens have been developed for recreational, agricultural and construction uses. These are but a few of the practically limitless examples of types of nonwovens and their uses that will be known to those skilled in the art who will also recognize that new nonwovens and uses are constantly being identified. There have also been developed different ways and equipment to make nonwovens having desired structures and compositions suitable for these uses. Examples of such processes include spunbonding, meltblowing, carding, and others which will be described in greater detail below. The present invention has general applicability to nonwovens as will be apparent to one skilled in the art, and it is not to be limited by reference or examples relating to specific nonwovens which are merely illustrative.
It is not always possible to efficiently produce a nonwoven having all the desired properties as formed, and it is frequently necessary to treat the nonwoven to improve or alter properties such as wettability by one or more fluids, repellency to one or more fluids, electrostatic characteristics, conductivity, and softness, to name just a few examples. Conventional treatments involve steps such as dipping the nonwoven in a treatment bath, coating or spraying the nonwoven with the treatment composition, and printing the nonwoven with the treatment composition. For cost and other reasons it is usually desired to use the minimum amount of treatment composition that will produce the desired effect with an acceptable degree of uniformity.
When a nonwoven web is formed of a hydrophobic material, for example, a polyolefin, it is often desirable to modify the surface of the nonwoven web using a hydrophilic surfactant to increase the wettability of the web. An external hydrophilic surfactant is typically applied to the surface of the nonwoven web. An internal hydrophilic surfactant is typically blended with the polymer used to form the nonwoven web, and later migrates to the surface after the nonwoven web is formed.
External and internal hydrophilic surfactants may be characterized in terms of their durability and wettability. The durability of a surfactant refers generally to its ability to withstand stresses, such as repeated washing cycles of the nonwoven fabric, without being removed from the fabric or otherwise losing its effectiveness. The wettability of a surfactant refers generally to its ability to transform a hydrophobic nonwoven web into a fabric which readily assimilates and distributes aqueous liquids. Surfactants which cause an otherwise hydrophobic nonwoven web to assimilate liquids at a relatively fast pace, with high fluid intake volumes, are referred to as faster wetting surfactants. Surfactants which cause the nonwoven web to assimilate aqueous liquids at a relatively slow pace, with low fluid intake volume, are referred to as slower wetting surfactants. In addition to the surfactant type, other factors affect the ability of the nonwoven web to assimilate liquids, including without limitation the nonwoven web type, nonwoven polymer type, fiber size and density, amount of surfactant, and how it is applied.
Surfactants having high durability are desirable for a variety of reasons.
However, durable surfactants often provide insufficient wetting, and do not lend themselves to optimization of wetting characteristics desired for individual end use applications. There is a need or desire for a surfactant composition having both durability and a faster rate of wetting. There is also a need or desire for a nonwoven fabric having durable wetting whose rate is relatively fast.